JP2020069517A - Solder alloy - Google Patents

Abstract

To provide a novel lead-free solder alloy that can be used in a high-temperature range.SOLUTION: A solder alloy includes Sn, Bi and Cu, where Sn content is 0.60 to 0.99 mass%, Cu content is 0.05 to 0.19 mass% and the balance Bi with inevitable impurities. In the solder alloy, the Sn content and the Cu content satisfy the following formulae: Cu content (mass%)≤1.61×Sn content (mass%)-0.92; and Cu content (mass%)≥1.50×Sn content (mass%)-1.29.SELECTED DRAWING: None

Description

  The present invention relates to solder alloys.

  Due to environmental considerations, the use of lead-free solder alloys is recommended. The temperature range of the solder alloy suitable for use as solder changes depending on the composition thereof.

  The power device is used as an element for power conversion in a wide range of fields such as hybrid vehicles and power transmission and transformation. Conventionally, Si chip devices could be used, but in fields where high breakdown voltage, large current applications, and high speed operation are required, SiC, GaN, etc., which have a larger band gap than Si, have been receiving attention in recent years.

  The conventional power module has an operating temperature of up to about 170 ° C., but next-generation SiC, GaN, etc. may reach a temperature range of 200 ° C. or higher. Along with this, heat resistance and heat dissipation are required for each material used for a module mounting these chips.

  Speaking of the bonding material, Sn-3.0Ag-0.5Cu solder is preferable from the viewpoint of Pb-free, but since the operating temperature may exceed 200 ° C in the next-generation type module, the melting point is around 220 ° C. More heat resistance is required than Sn-3.0Ag-0.5Cu solder. Specifically, from the viewpoint of the cooling of the radiator and the tolerance of the temperature around the engine, solder having a melting point of 250 ° C. or higher is required. The composition of the solder is represented by mass% unless otherwise specified. The Sn-3.0Ag-0.5Cu is Ag: 3.0 mass%, Cu: 0.5 mass%, and the balance Sn composition. That is. Although not subject to RoHS regulation, Pb solder (Pb-5Sn), which is not preferable from the viewpoint of environmental regulations, can handle the operating temperature of the next-generation module. Similar to Pb solder, Au-based solder (Au-Ge, Au-Si, Au-Sn) is used as the heat-resistant solder (Non-Patent Documents 1 to 3). Sn-based solder is known as an inexpensive solder (Patent Documents 1 and 2).

  Therefore, in recent years, a fine metal powder paste has attracted attention as a bonding material for next-generation modules. Due to the small size of the metal powder, the surface energy is high and sintering begins at temperatures well below the melting point of the metal. And, unlike solder, once sintered, it will not remelt unless the temperature is raised to near the melting point of the metal. Taking advantage of such characteristics, Ag fine powder paste is being developed (Patent Document 3).

  Although Pb-5Sn solder has a sufficient function as a bonding material for the next-generation power module, it is lead-containing and is preferably not used from the viewpoint of future environmental regulations. Further, although Au-based solder is desirable as a bonding material from the viewpoint of function and environment, it has a problem of material cost. Sn-based solder has a low melting point, and there is a possibility that the joint strength may be reduced in a high temperature environment such as 250 ° C. Further, the Ag fine powder paste can give sufficient bonding strength and heat resistance to the bonding layer depending on the conditions, but it has a problem of material cost.

  In the solder paste of Patent Document 4, a plurality of kinds of powders having different compositions are blended and designed to be an alloy after melting, but for that purpose, heating exceeding the melting point of each powder is required. For example, if Cu powder is used, complete melting cannot be expected unless it is heated to a melting point of Cu of 1084.6 ° C. or higher, and there is a concern of nonuniformity depending on the heating operation during soldering.

JP-A-9-271981 JP 2000-141079 A International publication WO2011 / 155055 International publication WO2007 / 055308

P. Alexandrov, W.M. Wright, M .; Pan, M.M. Weiner, L .; Jiao and J. H. Zhao, Solid-State Electron. 47 (2003) p. 263. R. W. Johnson and L.A. Williams, Mater. Sci. Forum 483-485 (2005) p. 785. S. Tanimoto, K .; Matsui, Y. Murakami, H .; Yamaguchi and H.M. Okumura, Proceedings of IMAPS HiTEC 2010 (May 11-13, 2010, Albuquerque, New Mexico, USA), p32-39.

  As described above, there has been a demand for a solder alloy having excellent properties even in a high temperature range required for a bonding material for a next-generation power module, for example, a temperature range exceeding 250 ° C.

  Further, according to the study by the present inventor, it has been found that a solder alloy which should have excellent properties often does not satisfy the intended properties. Such a phenomenon becomes a big problem in manufacturing.

  Therefore, an object of the present invention is to provide a solder alloy that does not contain lead added and can be used in a high temperature range, and is a novel solder alloy that can reliably exhibit intended properties. .

  As a result of earnest research, the present inventor has found that the above-mentioned object can be achieved by a Bi-based solder alloy described later, and arrived at the present invention.

Therefore, the present invention includes the following (1).
(1)
A solder alloy containing Sn, Bi, and Cu,
The Sn content is 0.60 to 0.99% by mass, the Cu content is 0.05 to 0.19% by mass, the balance is Bi and inevitable impurities, and the Sn content and the Cu content are Solder alloy that satisfies the following formula:
Cu content (mass%) ≦ 1.61 × Sn content (mass%) − 0.92
Cu content (mass%) ≧ 1.50 × Sn content (mass%) − 1.29

  According to the present invention, it is possible to obtain a solder alloy having excellent characteristics even in a high temperature range required for a bonding material of a next-generation power module, for example, a temperature range exceeding 250 ° C., without adding lead and containing lead. You can

FIG. 1 is an explanatory diagram illustrating a range of expressions that are simultaneously satisfied by Examples A and B of the present application.

  The present invention will be described in detail below with reference to embodiments. The present invention is not limited to the specific embodiments described below.

[Solder alloy]
The solder alloy of the present invention is a solder alloy containing Sn, Bi, and Cu, in which the Sn content is 0.60 to 0.99 mass% and the Cu content is 0.05 to 0.19 mass. %, With the balance being Bi and unavoidable impurities, Sn content and Cu content in the solder alloy satisfying the following formula:
Cu content (mass%) ≦ 1.61 × Sn content (mass%) − 0.92
Cu content (mass%) ≧ 1.50 × Sn content (mass%) − 1.29

  The solder alloy of the present invention is in a temperature range where both the solidus temperature and the liquidus temperature are high, and in order to maintain sufficient bonding strength even after holding for a long time at a high temperature, a bonding material for a next-generation power module. It has excellent properties even in a high temperature range required for the above, for example, a temperature range exceeding 250 ° C. In a preferred embodiment, the solder alloy of the present invention is advantageous from the viewpoint of future environmental regulations because lead is not intentionally added, and it is a material that does not use expensive Ag. It is also advantageous in terms of price.

  The unavoidable impurities are not the components intentionally added, but the components unavoidably mixed due to the material or process. For example, if the raw material metal is a 4N product, the maximum amount of unavoidable impurities is 0.01% by mass. In a preferred embodiment, the solder alloy of the present invention is a so-called lead-free solder alloy. It may be contained.

  The solder alloy of the present invention is a solder alloy that can reliably exhibit the intended properties. According to the studies conducted by the present inventors up to now, it has been found that a solder alloy that should have excellent properties often does not satisfy the intended properties. Such a phenomenon becomes a big problem in manufacturing. As a result of further study on the cause of this, it was found that the composition of the solder alloy often deviated from the planned composition. That is, it was found that the composition does not always match the composition expected from the ratio of the components prepared as raw materials. In order to prevent such compositional deviation, it is possible to precisely monitor the products produced by the manufacturing process and flexibly feed back and change the manufacturing conditions in real time. However, such a method has a problem that the process is complicated. Under these circumstances, the present inventor has arrived at the present invention by discovering a region of a composition that exhibits excellent properties and is less likely to cause compositional deviation. That is, the solder alloy of the present invention is a solder alloy that can surely exhibit excellent characteristics as intended by having the above composition range. The degree of the composition deviation can be confirmed by comparing the value of the composition charged during the production of the alloy with the value of the composition obtained by the ICP analysis value of the obtained alloy. It can be compared by calculating the value.

[Bi]
Bi (bismuth) is contained as a main constituent element of the solder alloy of the present invention. In a preferred embodiment, the content of Bi with respect to the solder alloy can be, for example, 98.82 to 99.35% by mass, preferably 98.82 to 99.16% by mass. In a preferred embodiment, the content of Bi with respect to the solder alloy can be, for example, 98.82 mass% or more, or, for example, 99.35 mass% or less, preferably 98.16 mass% or less. With such a range, the shear strength after 1000 hours at 250 ° C. can be further increased.

[Sn]
The Sn content with respect to the solder alloy may be, for example, 0.60 to 0.99% by mass, preferably 0.79 to 0.99% by mass. In a preferred embodiment, the Sn content with respect to the solder alloy can be, for example, 0.60 mass% or more, preferably 0.79 mass% or more, or, for example, 0.99 mass% or less. With such a range, the shear strength after 1000 hours at 250 ° C. can be further increased.

[Cu]
In a preferred embodiment, the Cu content with respect to the solder alloy can be, for example, 0.05 to 0.19 mass%. With such a range, the shear strength after 1000 hours at 250 ° C. can be further increased.

[Relationship between Cu content and Sn content]
In a preferred embodiment, the Cu and Sn contents satisfy the following formula:
Cu content (mass%) ≦ 1.61 × Sn content (mass%) − 0.92
Cu content (mass%) ≧ 1.50 × Sn content (mass%) − 1.29
In a preferred embodiment, the Cu and Sn contents satisfy the following formula:
Cu content (mass%) ≦ 1.50 × Sn content (mass%)-1.14
Cu content (mass%) ≧ 1.50 × Sn content (mass%) − 1.29

[Solidus temperature]
The solidus temperature can be, for example, 243 ° C. or higher, or 245 ° C. or higher. In the case of a solder alloy having a high solidus temperature (for example, 243 ° C. or higher), the shear strength after 1000 hours in a 250 ° C. environment is 30 MPa or higher, so that it can be sufficiently used in a high temperature range.

[Liquid line temperature]
The liquidus temperature can be, for example, 271 ° C. or lower.

[Liquid and solidus temperature]
In a preferred embodiment, the value of the following formula: [liquidus temperature]-[solidus temperature] (solidus liquidus temperature difference: PR) may be 28 ° C or lower, or 19 ° C or lower. it can.

[Preferable composition]
In a preferred embodiment, the composition of the solder alloy can be, for example:
Sn: Bi: Cu = 0.60-0.99% by mass: 98.82-99.35% by mass: 0.05-0.19% by mass and satisfying the following formula:
Cu content (mass%) ≦ 1.61 × Sn content (mass%) − 0.92
Cu content (mass%) ≧ 1.50 × Sn content (mass%) − 1.29
Sn: Bi: Cu = 0.79 to 0.99 mass%: 98.82 to 99.16 mass%: 0.05 to 0.19 mass% and a composition satisfying the following formula:
Cu content (mass%) ≦ 1.50 × Sn content (mass%)-1.14
Cu content (mass%) ≧ 1.50 × Sn content (mass%) − 1.29

[Joint strength]
The joint strength of the solder alloy can be measured by the means described in the examples. In a preferred embodiment, the bonding strength can be, for example, 47 MPa or more, or 49 MPa or more, preferably 52 MPa or more, as shear strength after one or three reflow treatments, for example, shear strength after one reflow treatment. .. “After three times of reflow” means that the process of performing the reflow process three times has been performed. Further, the shear strength after three times of reflow can be, for example, 49 MPa or more, or 52 MPa or more, preferably 55 MPa or more. In a preferred embodiment, the joint strength can be, for example, 30 MPa or more, or 42 MPa or more, and preferably 45 MPa or more, as the shear strength measured after holding for 1000 hours at 250 ° C. in an air atmosphere.

[Shape of solder alloy]
As the shape of the solder alloy of the present invention, a shape suitable for use as solder can be appropriately adopted. It may be a sheet-shaped member as described in the examples, and further may be a member in the shape of, for example, a wire, a powder, a ball, a plate or a rod. It is particularly preferable that the shape of the solder alloy is a powder shape, a solder ball shape (ball shape), or a sheet shape. The solder ball refers to a ball having a diameter of 50 μm to 500 μm, for example. In a preferred embodiment, the powder and the solder balls are collectively referred to as solder powder. The solder powder can be used for a solder paste, and in this case, for example, one having a particle size of less than 50 μm can be used.

[Preferred Embodiment]
In a preferred embodiment, the present invention includes the following (1) and the like.
(1)
A solder alloy containing Sn, Bi, and Cu,
The Sn content is 0.60 to 0.99% by mass, the Cu content is 0.05 to 0.19% by mass, the balance is Bi and inevitable impurities, and the Sn content and the Cu content are Solder alloy that satisfies the following formula:
Cu content (mass%) ≦ 1.61 × Sn content (mass%) − 0.92
Cu content (mass%) ≧ 1.50 × Sn content (mass%) − 1.29
(2)
The solder alloy according to (1), wherein the Bi content is 98.82 to 99.35% by mass.
(3)
(1)-(2) solder alloy whose solidus temperature is 243 degreeC or more.
(4)
(1)-(3) solder alloy whose liquidus temperature is 271 degreeC or less.
(5)
The following formula: [Liquid line temperature]-[Solid line temperature]
(1)-(4) solder alloy whose value of is 28 degrees C or less.
(6)
Solder alloys (1) to (5) having a joint strength of 47 MPa or more after one reflow treatment.
(7)
Solder alloys (1) to (6) having a joint strength of 49 MPa or more after three reflow treatments.
(8)
Solder alloys (1) to (7), which have a bonding strength of 30 MPa or more after being kept at a high temperature of 250 ° C. for 1000 hours.
(9)
(1) to (8) the solder alloy in which the shape of the solder alloy is powder, ball, or sheet.
(10)
(1) to (8) A member made of a solder alloy.
(11)
(1) to (8) Internal joint solder joints for electronic components soldered with a solder alloy.
(12)
(1) to (8) A power transistor solder joint soldered with a solder alloy.
(13)
(1) to (8) A printed circuit board having a solder alloy.
(14)
(1) to (8) An electronic component having a solder alloy.
(15)
(1) to (8) A power transistor having a solder alloy.
(16)
An electronic device having the solder joint according to (11) or (12), the printed circuit board according to (13), the electronic component according to (14), or the power transistor according to (15).
(17)
A power device having the solder joint according to (11) or (12).

  In a preferred embodiment, the present invention is a member made of the solder alloy, an internal joint solder joint of an electronic component soldered with the solder alloy, a solder joint of a power transistor soldered with the solder alloy, It includes a printed circuit board having the solder alloy, an electronic component having the solder alloy, and a power transistor having the solder alloy. In a preferred embodiment, the present invention includes an electronic device including the above solder joint, printed circuit board, electronic component, and power transistor, and includes a power device including the above solder joint.

  Hereinafter, the present invention will be described in detail with reference to examples. The present invention is not limited to the examples illustrated below.

[Study on Composition Deviation: Example A]
[Example A1]
A predetermined amount of Bi, Cu, and Sn chip raw materials were put into the graphite crucible, the graphite crucible was set in an atomizing device, and the atmosphere was maintained under an inert gas atmosphere for a certain period of time until the raw materials were uniformly dissolved to obtain a molten metal.
Then, the stopper installed at the bottom of the graphite crucible was pulled up, and the molten metal was dropped below. At that time, an inert gas was sprayed on the molten metal to produce solder powder.
0.5 g of solder powder was accurately weighed and dissolved in an acid, and then the concentration was measured by an ICP emission spectrophotometer. The results of the obtained composition values are shown in Table 1.
The ratio calculated from the amounts of Bi, Cu, and Sn charged as the raw materials is shown in Table 1 as the charged composition.
From the composition and the ICP analysis value, the following formula:
Composition ratio [%] = {[ICP analysis value (mass%)] / [prepared composition value (mass%)] × 100
The value of the composition ratio [%] was determined by. When the value of this composition ratio (ICP / prepared composition ratio) is 100%, it means that there is no composition deviation. The results are also shown in Table 1.

[Examples A2 to A12]
Solder powder was produced from the raw materials in the same manner as in Example A1. Table 1 shows the charged composition value and the composition value by ICP analysis.

[Comparative Examples A1 to A10]
Solder powder was produced from the raw materials in the same manner as in Example A1. Table 1 shows the charged composition value and the composition value by ICP analysis.

[Results of Example A]
In the examples, the difference between the charged composition and the ICP analysis value of the produced alloy powder was as small as about several percent. On the other hand, in the comparative example, these differences were very large, about several tens of percent.

[Examination of shear strength: Example B]
[Example B1]
A predetermined amount of Bi, Cu, and Sn chip raw materials were put into the graphite crucible, the graphite crucible was set in an atomizing device, and the atmosphere was maintained under an inert gas atmosphere for a certain period of time until the raw materials were uniformly dissolved to obtain a molten metal.
Then, the stopper installed at the bottom of the graphite crucible was pulled up, and the molten metal was dropped below. At that time, an inert gas was sprayed on the molten metal to produce solder powder.
0.5 g of solder powder was accurately weighed, dissolved in an acid, and then the concentration was measured by an ICP emission spectrophotometer. The results are shown in Table 2.

[Measurement of solidus temperature, liquidus temperature, melting point]
The solidus temperature (SPT), the liquidus temperature (LPT) and the melting point (MP) of the solder alloy are measured according to JIS Z3198-1: 2014, and the method is based on differential scanning calorimetry (DSC). It was carried out in. The results are summarized in Table 2.

[Measurement of shear strength (1 or 3 times of reflow)]
An Al surface (thickness: 3 μm) was formed on one surface of the Si wafer by sputtering, and a polyimide film was further formed by coating, and then a land having a 300 μm diameter opening was formed in the polyimide film by exposure and development.
Further, a Ni layer (thickness 2.5 μm), a Pd layer (thickness 0.05 μm), and an Au layer (thickness 0.02 μm) were sequentially formed on the land portion by electroless plating to provide the UBM.
Flux was applied on the UBM, solder powder of 300 μmΦ was further mounted on the UBM, reflow treatment was performed, and heat bonding was performed. The conditions for the reflow treatment were that the reflow temperature was 290 ° C. × 1 minute, and this was performed only once or repeated three times.
After that, the bonding strength (shear strength) was measured under the following conditions.
The bonding strength was measured according to MIL STD-883G. The tool attached to the load sensor descends to the board surface, the device detects the board surface and stops descending, the tool rises to the set height from the detected board surface, and the tool pushes the joint to destroy the board. The load was measured. The results are summarized in Table 2.
<Measurement conditions>
Device: dage series 4000 manufactured by dage
Method: Die shear test Test speed: 100 μm / s
Test height: 20.0 μm
Tool movement amount: 0.9 mm

[Measurement of shear strength (after high temperature test)]
After the reflow treatment (one time of the reflow treatment), as a high temperature test, after holding at 250 ° C. for 1000 hours in an air atmosphere, the shear strength was measured in the same manner as above. The results are summarized in Table 2.

[Examples B2 to B5]
Solder powder was prepared in the same procedure as in Example B1, the concentration was measured with an ICP emission spectrophotometer, and the solidus temperature, liquidus temperature and melting point were measured by differential scanning calorimetry, and one reflow was performed. Then, the shear strength was measured after three reflows and after the high temperature test. The results are summarized in Table 2.

[Comparative Examples B1 to B8]
In the same procedure as in Example 1, solder powder was prepared, the concentration was measured with an ICP emission spectrophotometer, and the solidus temperature, liquidus temperature and melting point were measured by differential scanning calorimetry, and one reflow was performed. Alternatively, the shear strength was measured after three times and after the high temperature test. The results are summarized in Table 2.

[Results of Example B]
As shown in Table 2, the solder alloys of Examples B1 to B5 maintained sufficient shear strength even after 1000 hours at 250 ° C.

In Table 2, Comparative Examples B2, B4, B6 and B8 were already too low in shear strength after 3 times of reflow.
Comparative Examples B1, B3, B5, and B7 had solid phase temperatures that were too low. Therefore, the shear strength was not measured because it was considered insufficient as a solder alloy.

  Compared with Comparative Example B2, Examples B1 and B2 had substantially the same Cu content but different Sn contents, so that the shear strength after one reflow and after three reflows was significantly improved. Was becoming. Similarly, Example B3 was compared with Comparative Example B4, and Examples B4 and B5 were compared with Comparative Example B6, but the Cu content was almost the same, but the Sn content was different. The share strength after three reflows was greatly improved.

[Summary of Results of Example A and Example B]
As shown in Table 2, the solder alloys of Examples B1 to B5 were such that the composition thereof had a certain regular range. The formula showing this range is shown below. The range represented by the following equation is shown in FIG. The range shown in FIG. 1 simultaneously satisfies the results shown in Tables 1 and 2, that is, the preferable ranges clarified from Example A and Example B.

The composition range of the solder alloy shown in FIG. 1 satisfied the following ranges:
0.60 ≦ Sn content (mass%) ≦ 0.99
0.05 ≦ Cu content (mass%) ≦ 0.19
Cu content (mass%) ≦ 1.61 × Sn content (mass%) − 0.92
Cu content (mass%) ≧ 1.50 × Sn content (mass%) − 1.29

In Examples A and B, the following combinations have the same ICP analysis values:
Example A2 = Example B1
Example A3 = Example B2
Example A6 = Example B3
Example A9 = Example B4
Example A10 = Example B5
Example A1 = Comparative example B2
Example A4 = Comparative Example B3
Example A5 = Comparative example B4
Example A7 = Comparative example B5
Example A8 = Comparative example B6
Example A11 = Comparative Example B7
Example A12 = Comparative Example B8

  The present invention provides a solder alloy having excellent properties in a high temperature range. The present invention is an industrially useful invention.

Claims (17)

A solder alloy containing Sn, Bi, and Cu,
The Sn content is 0.60 to 0.99% by mass, the Cu content is 0.05 to 0.19% by mass, the balance is Bi and inevitable impurities, and the Sn content and the Cu content are Solder alloy that satisfies the following formula:
Cu content (mass%) ≦ 1.61 × Sn content (mass%) − 0.92
Cu content (mass%) ≧ 1.50 × Sn content (mass%) − 1.29.   The solder alloy according to claim 1, wherein the Bi content is 98.82 to 99.35% by mass.   The solidus temperature is 243 degreeC or more, The solder alloy in any one of Claims 1-2.   The solder alloy according to claim 1, which has a liquidus temperature of 271 ° C. or lower. The following formula: [Liquid line temperature]-[Solid line temperature]
The solder alloy according to any one of claims 1 to 4, which has a value of 28 ° C or less.   The solder alloy according to any one of claims 1 to 5, which has a bonding strength of 47 MPa or more after one reflow treatment.   The solder alloy according to any one of claims 1 to 6, which has a bonding strength of 49 MPa or more after three reflow treatments.   The solder alloy according to any one of claims 1 to 7, which has a bonding strength of 30 MPa or more after being kept at a high temperature of 250 ° C for 1000 hours.   The solder alloy according to any one of claims 1 to 8, wherein the solder alloy has a powder shape, a ball shape, or a sheet shape.   A member made of the solder alloy according to claim 1.   An internal joint solder joint of an electronic component soldered with the solder alloy according to claim 1.   A solder joint for a power transistor soldered with the solder alloy according to claim 1.   A printed circuit board comprising the solder alloy according to claim 1.   An electronic component comprising the solder alloy according to claim 1.   A power transistor comprising the solder alloy according to claim 1.   An electronic device comprising the solder joint according to claim 11 or 12, the printed circuit board according to claim 13, the electronic component according to claim 14, or the power transistor according to claim 15.   A power device having the solder joint according to claim 11.

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